Liquid slip regulator



' Jan. 9, 1945.

C. B. HUSTON LIQUID SLIP REGULATOR Filed Sept. 23, 1943 [MA 29a Y Inventor: Claude B. H uston,

His Attorney,

I Patented Jan. 9, 1945 V UNITED. STATES PATENT OFFlCE LIQUID SLIP REGULATOR clause 13. Huston, Schenectady, N. r, minimto General Electric Company, a corporation of New York Application September 23, 1943, Serial No. 503,491

Claims.

Heretofore, liquid slip regulators have been;

equipped with alternating current torque motors for raising the movable electrodes. These torque motors were supplied from series current transformers connected inthe primary circuit of the controlled induction motor.

The alternating current torque motors used in liquid slip regulators were not of a standard construction but were specially designed in that they were provided with very small, special shaft ball bearings, and were further provided with flexible leads instead of slip rings and brushes foruthe purpose of reducing friction losses to a minimum.

The principal use made of current transformers is in connection with relaying operations and measurements. For these uses current transformers of 100-volt ampere ratings are adequate, and consequently, current transformers in larger ratings are not built as a standard lineof apparatus. Current transformers having ratings of the order of 3000-volt amperes were'required for supplying the torque motor of a liquid slip regulator. Furthermore, it was necessary to design the current transformers specially to match the rating of the induction motor with which the regulator was used and the rating of the specially designed torque motor, with the result that a different transformer was required for each installation. Apparatus which is specially designed and constructed is more expensive than standard line apparatus which is produced in large-quan- 1 titles.

Another disadvantage of liquid slip regulators used heretofore was that the connections of the current transformer in vthe high voltage line to the induction motor with which the regulator was used made it necessary to house the transformer in an expensive metal-clad container, to maintain the standards of metal-clad construction.

Accordingly,,a more specific object of this invention is the provision of a liquid slip regulator which is constructed of standard parts, such as small instrument type current. transformers, direct current motors and exciters, thereby substantially to lessen the cost of the regulator without sacrificing anything in performance.

\A further disadvantage of earlier slip regulators was the inconvenience of changing taps on the large current transformer or varying the counterweight to make adjustments for different load settings, and a, further object of this invention is the provision of a slip regulator in which such adjustments are made by varying a small potentiometer type resistor.

5 A still further disadvantage of slip regulators used heretofore was the necessity of providing an auxiliary motor inadditio'n to the alternating current torque motor and an auxiliary weight in addition to the counterweight for raising the movable electrodes to the maximum resistance position prior to connecting the controlled induction motor to the source. Thus. 9. still further object of this invention is the provision of a control for a liquid slip regulator which eliminates, this auxiliary starting apparatus and provides for the utilization of the regulating torque motor to raise the movable electrodes to effect the maximum separation prior to connecting the controlled motor to the source.

In carrying th invention into eflect in one form thereof, a direct current motor of aconventional design is provided for moving the movableelectrodes. It is supplied from a COD-V611. tional motor generator set of which the generator'voltage is varied by means of an exciter which is excited by means of a conventional, small instrument type current transformer in the primary circuit of the controlled induction motor. This current transformer may be one which is being relaying operations.

- If desired, the exciter may be a high speed, armature reaction excited machine. This type of exciter is also of a standard design which is made in large quantities at low .cost.

For a better understanding of the invention, reference should now be had to the following specification and to the accompanying drawing of which the single figure is a simple, diagrammatical sketch of an embodiment of the invention.

Referring now to the drawing, the primary winding of a polyphase alternating current motor l0 which is illustrated as an induction motor of the wound rotor type is supplied from a suitable polyphase source, such as represented by the three supply lines H to which the primary winding of the motor may be connected by suitable cult breaker l2. This circuit breaker may be. and preferably is, of the oil circuit breaker type. The motor I0 is provided with a flywheel l3 of suitable dimensions.

The peakdemand of the induction motor I! is to be limited by automatically inserting reutilized in connection with measurements or switching means which are illustrated as a cirslstance in the secondary circuit of the motor. This reduces the speed and permits the stored energyinthefiywheeltocarrythepeakload. When the demand subsides, the induction motor accelerates and again stores energy in the fiywheel.

For the purpose of inserting resistance in the secondary circuit of induction motor III, a liquid rheostat I4 is provided. This liquid rheostat i4 comprises a tank ll whichvcontains a solution of sodium carbonate and a plurality of stationary electrodes It. l1, and it and a plurality of cooperating movable electrodes ll, 20. and 2|. The stationary electrodes It, l1, and II are mounted within the tank at the bottom thereof. The upper or movable electrodes are fastened to a crossarm 22 which constitutes the Y-point of the secondary circuit.

To the top of the tank It is secured a suitable truss-shaped superstructure 23 upon which a pulley 24 is rotatably mounted in a position above the crossarm 22. A cable "is fastened to the crossarm 2!. This cable passes over the pulley I4 and about a drum 26 to a, counterweight 21. The weight of the electrodes I9, 20, and ii and the crossarm supporting structure is such a to overbalance the counterweight 21 and move to the bottom of thetank to reduce the secondary resistance in the circuit of motor III.

For the purpose of raising the movable electrodes to increase the resistance of the liquid rheostat, a direct current torque motor II is provided. This motor is supplied from an ad- Justable voltage direct current generator 29 which is driven at a speed which is preferably substantially constant by suitable means, such as an induction motor (not shown). The armatures of the torque motor 28 and the adjustable voltage generator 29 are connected in a direct loop circuit, as indicated in the drawing. The torque motor 2| is provided with a separately excited shunt field winding Ila which is supplied from a suitable source of excitation (not shown). The generator 28 is also provided with a separately ezrcited'field winding 28a. Variable excitation is supplied to this field winding 28a by means of a suitable exciter, such as the armature excited dynamoelectric machine 30. This machine is driven at a speed which is preferably substantially constant by any suitable driving means such as an induction motor (not shown).

The armature reaction excited machine ill is provided with a pair of load brushes Illa and a pair of short-circuited brushes 30b which are arranged on an axis which is displaced 90 electrical degrees from the axis of the load brushes. The dynamoelectric machine 30 is provided with a plurality of control field windings 30c, 39d, and "e. The control field winding 300 is supplied from a suitable source of excitation represented by the supply lines II and 32. This source may be, and preferably is, the same source as that from which the field winding 28a of the torque motor is supplied. The polarity of the excitation of the-control field winding 30a is such that the excitation supplied by the dynamoelectric machine to the field winding 29a causes the generator 29 to supply current to the torque motor 28 in a direction which causes the torque motor II to tend to raise the electrodes it, 20, and ii. The field winding "c is referred to as the bias field winding.

The field winding 30d is excited from the terminals of the adjustable voltage generator 2! to which it is connected by means of conductors 34 and It. Thus, the control field winding Ila is responsive to the voltage of the generator 2| and is referred to as the voltage control winding. A plurality of resistors 36, 31, I8, and 3! are connected in series relationship with the voltage field winding Md. The connections of the voltage field winding Illd to the terminals of the generator II are such that the voltage winding Ila opposes the bias field windinglllc.

The field winding We is excited in accordance with the load current of the main wound rotor induction motor III. This is accomplished by connecting the field winding the to the output terminals of a rectifier 40, of which the input terminals are connected to the terminal Ho and the slider 4": of a potentiometer 4i which is connected across the secondary winding 42 of a current transformer, of which the primary winding carries the load current supplied to one phase of the primary winding of the motor l0. Since the control field winding Illc is excited in accordance with the load current supplied to the induction motor I0, it is referred to as the load control field winding. The polarity of the load control field winding m is the same as the polarity of the bias control field winding lie.

The armature reaction along the load brush axisis neutralized by means of a series compensating field winding The net excitation along the load brush axis produced by the control field windings produces a fiux which causes current to flow in the short circuit. This short circuit current produces an armature fiux which generates a voltage across the load brushes "a and causes current to flow in the load circuit. The machine is thus a cross armature flux excited direct armature flux compensated dynamoelectric machine. The important characterisics of this machine are its high speed of response and its high amplification factor, 1, e., the ratio of the current in the load circuit to the current in the control field windings.

The value of the load current supplied to the induction motor I 0 can be adjusted by adjustment of the/potentiometer 4|.

The raising of the movable electrodes i9, 20, and 2| prior to the closing of the main circuit breaker 12 .to start the induction motor I0 is under the control of a manually operated switching device 43 and a relay 44 which is directly controlled by the' manually operated switching device 43. A limit switch 45 on the liquid rheostat and a relay 46 controlled thereby cooperate with the manually operated switching device 43 to close the main circuit breaker I2 to connect the induction motor ID to the source.

The opening of the circuit breaker l2 to disconnect the motor iil from the source is also under the control of the manually operated switching device 43.

For the purpose of rapidly braking the induction motor it to rest after it has been disconnected from the supply source ll means are provided for producing a dynamic braking torque. These means are illustrated as a circuit breaker 41 which, when operated to its closed position, connects two phases of the induction motor it to a D.-C. source. The closing of the dynamic braking circuit breaker 41 is under the control of a manually operated switching device 40, a relay 4! controlled thereby, and contacts on the limit switch relay 45.

With the foregoing understanding of the elemerits and their organization, the operation of the liquid slip regulator to limit the load current supplied to the main induction motor III to a predetermined maximum value will readily be understood from the following detailed descriptions:

When the induction motor is at rest, the movable electrodes I9, 20, and 2| are in their lowermost position in the tank l5, and the resistance of the secondary circuit or the induction motor III is a minimum. With the main oil circuit breaker I: in the open position and the manually operated switching device 43 in the off position as illustrated in the drawing, the relay 50.

- from one side of a D.-C. source which may be,

and preferably is, the same as that represented by the two supply lines 3| and 32, through nor-.

mally closed interlocks on the circuit breaker l2, operating coil of therelay 50 to the negative side of the D.-C. supply source. Responsiv'ely to-energization, the relay 50 closes its upper and lower normally open contacts 50a and 53b and opens its normally closed contacts 500. Contacts 50a in closing complete the connections of the bias fieldwinding 30c of'the armature reaction excited dynamoelectric machine 30 to the source 3|, 32, and the contacts 501), in closing, shortcircuit the resistor section 39 in the circuit of the voltage field winding 30d. The opening of contacts 500 inserts the adjustable resistor section 36 in the circuit of the voltage field winding 30d. The resistor sections 31 and 38 in the circuit of the voltage field winding 30d are shortcircuited by the normally closed contacts a of relay 44. Thus, the resistor 36 is the only resistance in the circuit of the voltage field winding at this instant.

The excitation of the bias field winding 300 causes the exciter machine 30 to supply 9. voltage to the" separately excited field winding 29a of the adjustable voltage generator 29. As the voltage of the generator 29 increases, the voltage field winding 30d which is excited difierentially with respect to the field winding 30c increases until a condition of balance is reached such that any further increase in the excitation of the field winding 30d would tend to reduce the excitation oi the adjustable voltage generator 29. When this condition of balance is reached, the adjustable voltage generator 29 supplies approximately 80 per cent of normal full load current to the armature of the torque motor 28. At this value of armature current, the torque developed by the torque motor 28 is insufllcient to raise the electrodes I9, 20, and 2|.

To raise the electrodes and connect the induction motor II) to the source the'manually operated switching device 43 is moved from the central off position to the closed position at the right. In this position, the movable contact members 43a and 43b engage the stationary contact members 43;; and 43d respectively. The engagement of contacts 43b and 43d completes an energizing circuit for the operating coil of the relay 44 which picks up and closes its upper normally open contacts b to short-circuit the adjustable resistor 36 and opens its lower normally closed contacts a to insert the resistor sections 31 and 3B in the circuit of the voltage field winding 3011. The short circuitingof the resistor section 36 tends to strengthen the voltage field 30d, but the insertion oi the resistors 31 and 38 weakens the field more than it is strengthened. Thus,

the opposing eflect' oi the field winding 30d is lessened. and. the net excitation of the. armature excited dynamoelectric machine 30 is increased. As a result, the voltage or the adjustable voltage generator 29 is further increased, and the current which is supplied to the torque motor 28 the voltage of the generator 29 is such that ap-- proximately per cent of full load current is supplied to the torque motor 28.

The torque developed by the torque motor 28 at 100 per cent full load current, together with the torque produced on the drum 26 by the counterweight 21, is suflicient to raise the movable electrodes I 9, 20, and 2| and as a result, the movable electrodes are moved toward the upper or maximum resistance position.

When the electrodes reach their upper or maximum resistance position, the limit switch 43 closes the normally open contacts 45a to complete an energizing circuit for the operating coil or the limit switch relay 8. The relay 46 in picking up closes its normally open contacts 46a, 46b, and 6c. The contacts 46a in closing complete an energizing circuit for the operating coil of relay 5|. with an adjustable time delay device such as the dashpot 5 la which introduces a time delay in the dropout of relay 5| but permits it to pick up without time delay. Consequently, the relay 5| picks up without time delay and closes its normally open contacts 5") to complete an energizing circuit for theoperating coil |2a of the circuit breaker |2. In response to energization, the circuit breaker l2 closes its main contacts to connect the primary winding of the induction motor H) to the-supply source II and simultaneously opens its auxiliary interlock contact l2b. Circuit breaker l2 in closing latches itself in the closed position by means or latching mechanism I20. Contacts |2b in opening interrupt the energizing circuit for the operating coil of the relay 6| which after a timevinterval determined by the adjustment of the time delay device 5|a drops out and opens its main contacts- 50b to interrupt the energizing circuit for the operating coil |2a of circuit breaker l2. The circuit breaker, however, is held closed by the latching mechanism |2c. The manually operated switching device 43 may now be released, and its. centering springs return it to the central or oil? position.

Contacts |2b of the circuit breaker |2 in opening also interrupt the energizing circuit for the operating coil of relay 50. In response to deenergization, relay 50 drops out and opens its normally open contacts 50a and 50b and closes its normally closed contacts 500. The opening of contacts 50b inserts resistor 39 in circuit with the voltage control field winding 30d, and the closing oi contacts 500 short-circuits resistor section 36. The opening of contacts l2b also interrupts the energizing circuit for the operating coil of relay 4 which drops out to close its normally closed contacts d and to open its normally open contacts b. Contacts d in closing short circuit resistor sections 38 and 39. Thus at this instant only the resistor section 39 is in circuit with the voltage control field winding.

The opening of contacts 50a disconnects the bias control tleld winding 300 from the source 3|. 32. Simultaneously, however, the load field As illustrated. this relay is provided.

winding We is energized by a current which is proportional to the current supplied from the source II to the primary winding of the induction motor ll. Since the inrush current to the motor II is limited by the maximum resistance or the liquid rheostat II, the current supplied to the load field winding 30 is aminirnum. Consequently, the net excitation of the armature reaction excited dynamoelectric machine 30 is decreased and this results in decreasing the current supplied to the torque motor 28 below the value which is sufilcient to maintain the movable electrodes is, Ill, and ii in the upper limit position As a result, the movable electrodes I8, 20, and II start to descend. As the separation between the movable electrodes and the stationary electrodes decreases, the resistance in the secondary circuit of the induction motor it is correspondingly decreased, and the current taken by the primary winding from the source Ii is correspondingly increased.

At a predetermined value oi load current taken by the induction motor II, which value is determined by the position of the slider lb on the potentiometer li, a condition of balance is reached in which the exciting current supplied to the load field winding 30c increases the net excitation of the dynamoelectric machine 30 to a value at which the torque developed by the torque motor 28 is sumcient when added to the pull or the counterweight 21 to arrest the descent of the movable electrodes.

The induction motor I. is accelerated by this maximum value of current which can be taken from the supply source II and as it accelerates, it stores energy in the flywheel it.

As long as the demand or the load on the induction motor Ill remains less than the maximum load as determined by the setting of the potentiometer ll, the motor drives the load without taking any energy from the flywheel l3. Consequently, it the peak demand of the load is greater than the value of maximum load current determined by the setting of the potentiometer ll, the tendency of the induction motor Ill is to decrease its speed and draw more current from the line. The increase in current immediately strengthens the net excitation oi the dynamoelectrlc machine 30 and ultimately, the torque oi the torque motor 28. In response to the increased torque oi the torque motor, the movable electrodes i9, 20, and II are moved upward to increase the resistance in the secondary circuit of the induction motor Ill, and prevent the induction motor Ill from drawing more than the predetermined maximum value of current irom the line ll. Consequently, the speed of the induction motor ll decreases and the flywheel ll then carries the load at the decreased speed.

when the load on the induction motor ill decreases, the opposite action results. As the torque of the torque motor 28 decreases, the movable electrodes descend toward the stationary electrodes, thereby cutting out resistance. Thereupon, the speed of the induction motor ll increases so that the stored energy given up by the flywheel is again restored to the flywheel.

This action is repeated whenever the load imposed on the shaft of the induction motor Ill exceeds the maximum load current setting of the potentiometer ll.

In order to minimize overshooting or hunting of the regulator, suitable antihunt means are provided. This means comprises a transformer I! having its primary winding 52a connected across the load brushes Illa oi the armature reaction excited dynamoelectrie machine Ill and having its secondary winding connected in a parallel loop circuit with the bias control field winding 300. Thus, when the voltage supplied to the torque motor 28 by generator 29 is changing as a result of a change in the output voltage or dynamoelectric machine ill, a voltage which is proportional to the rate of this change is induced in the secondary winding 52b 01' trans iormer 52. This secondary induced voltage is supplied to the bias control field winding tile in a direction which opposes the change. As a resuit, the rate of change of the output voltage of dynamoelectric machine 30 is decreased before the final value is attained, and thus, overshooting or hunting is substantially eliminated.

To stop the motor Iii, the manually operated switching device 43 is rotated counterclockwise from the central position to the trip position. In this position, an energizing circuit is completed for the operating coil oi the tripping relay II. In response to energization, the core 0! relay '3 is moved upward to release the latching mechanism lie and allow the spring lZd to open the circuit breaker i2 and thereby disconnect the motor ill from the supply source II.

In the open position of circuit breaker it, an energizing circuit is completed for the operating coil of relay 50 through the normally closed interlock contacts lib. Responsively to energization, relay 50 closes its contacts 50a and 50b and opens contacts 500. Contacts 500 in closing reconnect the bias control field winding 300 to the supply source Ii, 32. At this time the load control field winding Slle is deenergized owing to the disconnection of motor ill from the source -ll. Contacts b in closing short-circuit the resistor I! in the circuit of the voltage control field winding of dynamoelectric machine It. Since the resistors 31 and 38 are short-circuited by the contacts a of relay 44, the voltage control field winding 30d is strengthened to a value at which it overpowers the bias control field winding Ilic. As a result, the output voltage oi the dynamoelectric machine 30 is reversed. This reversal of the output voltage of dynamoelectric machine 30 forces the excitation of generator 2| to decrease very rapidly. As the voltage of generator 29 decreases, the current supplied to the torque motor 28 and the torque developed thereby decrease correspondingly. As a result, 'the pull oi the counterweight 21 plus the decreased torque of the torque motor 28 is no longer sufficient to maintain the electrodes I 9, 20, and II in a raised position, and consequently, theydescend to the minimum resistance position at the bottom of the tank.

As the voltage or the generator 28 decreases, the excitation of the voltage control field wind ing decreases so that the polarity oi the output voltage of the armature reaction excited dynamoelectric machine is again determined by the bias control field winding No.

If it is desired to brake the induction motor it rapidly to rest, the manually operated switching device 8 is rotated in a clockwise direction to the closed position. In this position, energizing circuits are established for the operating coils of relays l4 and 49. In response to energization, relay 44 picks up to open its contacts a and close its contacts b. In closing, the contacts b short-circuit the resistor 36, thereby tending to strengthen the voltage field lld, but contacts a in opening insert the resistors complete an energizing circuit for the operating coil of the limit switch relay 46 which picks up and closes its contacts 46a, 46b, and 48c.

Contacts 48b in closing complete an energizing circuit for the operating coil of the dynamic braking relay 49 which in response to energization picks up and closes its contacts to complete an energizing circuit for the operatin coilof the dynamic braking circuit breaker 41. In response to energization, dynamic braking circuit breaker 41 closes its contacts to connect a portion of the primary winding of induction motor III to asource of direct current excitation. This direct current excitation of a portion of the induction motor winding produces a large braking torque which rapidly brakes the induction motor to rest. It will be-noted that the switching device 48 need only be held in the closed position momentarily to allow the latching mechanism 41a to latch the dynamic braking circuit breaker 41 in the closed position.'

After the induction motor ID has been braked to rest, the primary winding of the induction motor may be disconnected from the source of direct current excitation by rotating the manually operated switching device in a counterclockwise direction to complete an energizing circuit for the operating coil of the trip relay 41b. This relay in response to energization releases the latching mechanism 41a, thereby allowing the circuit breaker 41 to drop to the'open position.

Although in accordance with the provisions of the patent statutes this invention is described as embodied in concrete form and the principle thereof has been explained, together with the best mode in which it is now contemplated applying that principle, it will be understood that .the apparatus shown and described is merely illustrative and that the invention is not limited thereto, since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims. a

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A liquid slip regulator for an induction motor comprising a tank containing anelectrolyte and relatively movable electrodes connected in circuit with said motor, a direct current motor for varying the separation of said electrodes, an adjustable voltage generator for supplying said motor, means for exciting said generator comprising a dyr' moelectric machine provided with a load control field winding, and means responsive to the current supplied to said alternating current motor for exciting said control field winding.

2. A liquid slip regulator for an induction mtor comprising a tank containing an electrolyte and relatively movable electrodes connected in circuit with said motor, a direct current motor for varying the separation of said electrodes, an

adjustable voltage generator for supplying said motor, means for exciting said generator comprising a dynamoelectric machine provided with a load control field winding, and means for supplying to said control field winding 9. direct voltage derived from the alternating current suppl ed to said induction motor.

3. A liquid slip regulator for an alternating current motor comprising in combination a tank containing an electrolyte and a plurality of relatively movable electrodes in circuit with said motor, a direct current motor for varying the separation of said electrodes, an adjustable voltage generator i'or supplying said direct current motor, means for exciting said generator provided with a load control field winding and an opposing field winding energized by the voltage of said generator, and means for supplying to said control field winding a direct voltage derived from the current supplied to said alternating current motor.

4.- A liquid slip regulator for an alternating current motor comprising in combination a tank containing an electrolyte and a plurality of relatively movable electrodes in circuit with said motor, a direct current motor for varying the separation of said electrodes, an adjustable voltage generator for supplying said direct current motor, means for exciting said generator comprising a dynamoelectric machine providedwith a separately excited field winding and an opposing field winding energized by the voltage of said generator, a switching device, and means responsive to operation oi said switching device for weakening the excitation of said opposing field winding to increase the voltage of said generator thereby to cause said motor to separate said electrodes.

5. A liquid slip regulator for an induction motor comprising in combination a tank containing an electrolyte and a plurality of relativel movable electrodes in circuit with said motor, a direct current motor for varying the separation 01 said electrodes, an adjustable voltage generator for supplying said direct current motor. means for exciting said generator comprising a dynamoelectric machine provided with a separately excited control field winding, an opposing control field winding excited by the voltage of said generator, and a. load control field winding excited by a current derived from the current supplied to said induction motor, a switching device, means responsive to operation of said switching device for weakening said opposing field to strengthen the voltage of said generator and cause said direct current motor to separate said electrodes, and limit switch means responsive to a predetermined separation of said electrodes for deenergizing said separately excited field winding and for connecting said induction motor to a source of alternating current.

6. A liquid slip regulator for an induction motor comprising in combination a tank for containing an electrolyte and a plurality of relatively movable electrodes, a direct current motor for varying the separation of said electrodes, an adjustable voltage generator for supplying said rect current motor, means for exciting said generator comprising a dynamoelectric machine provided with a separately excited control field winding, an opposing field winding excited b the voltage of said generator and a loadcontrol field winding, a current transformer energized by the load current of said induction motor, and a rec tifier in circuit with said transformer for exciting said load control field winding in the same direction as said separately excited field winding, a switching device, means responsive to operation of said switching device for varying the relative excitations oi said separately excited and opposing control field windings to increase the voltage oi said generator to cause said motor to separate said electrodes, and limit switch means responsive to a predetermined separation of said electrodes for deenergizing said separately excited field winding and connecting said induction motor to an alternating current source to provide for excitation of said dynamoelectric machine by the diflerential eflect oi the loa on said induction motor and the voltage of said generator.

I. A liquid slip regulator for an induction motor comprising in combination an electrolyte container, a plurality of relatively movable electrodes within said container, a direct current motor for varying the separation of said electrodes, an adjustable voltage generator for supplying said direct current motor, means for exciting said generator comprising a dynamoelectric machine provided with a control field winding connected to be excited by a direct voltage derived from the alternating current supplied to said induction motor and an opposing field winding excited by the voltage oi said generator to cause said motor to vary the separation oi said electrodes to limit the current supplied to said induction motor to a predetermined value, and means for adjusting said derived voltage to a value corresponding to a desired limiting value of current supplied to said induction motor.

8. A liquid slip regulator comprising in combination, an electrolyte container, a plurality of relatively movable electrodes within said container, a direct current motor for varying the separation oi said electrodes, an adjustable voltage generator for supplying said direct current motor, means for exciting said generator comprising a dynamoelectric machine provided with a separately excited field winding and an opposing field winding excited by the voltage of slid generator to effect energization of said generator of a polarity to cause said motor to effect separation of said electrodes, and a transformer having its primary winding connected across said generator and its secondary winding connected in circuit with said separately excited field winding to minimize hunting action or said slip regulator.

9. A liquid slip regulator for an induction motor comprising in combination an electrolyte container, a plurality oi relatively movable electrodes within said container, a direct current electric motor for varying the separation oi said electrodes, an adjustable voltage generator for supplying said motor, means for exciting said generator comprising a dynamoelectric machine provided with a separatel excited control field winding, an opposing control field windin excited by the voltage of said generator and a load control field winding excited by a current derived irom the current supplied to said induction motor and having the same polarity as said separately excited field winding, a switching device, means responsive to operation of said switching device for weakening said opposing field to cause said direct current motor to separate said electrodes, limit switch means responsive to a predetermined separation oi said electrodes ior deenergizing said separately excited field winding and connecting said induction motor to an alternating current source so that said load control field winding and said opposing control field winding control said dynamoelectric machine to limit the current supplied to said induction motor to a predetermined value, and a transformer having its primary winding connected across said generator and its secondary winding connected to said separately excited field winding to minimize hunting action of said regulator.

10. A liquid slip regulator for an induction motor comprising in combination, an electrolyte container, a plurality of electrodes within said container, a direct current motor for varying the separation of said electrodes, an adjustable voltage generator ior supplying said direct current motor, means for exciting said generator comprising a dynamoelectric machine provided with a load control field winding connected to b excited in response to a voltage derived from the current supplied to said induction motor, an opposing control field winding excited in response to the voltage of said generator and a separately excited field winding, means for deenergizina said induction motor to eiIect stopping thereof, a switching device, means responsive to operation of said switching device for connecting said separately excited field winding to a source of excitation and weakening the strength of said opposing control field winding to cause said direct current motor to rotate to separate said electrodes, and limitiswitch means responsive to a predetermined separation of said electrodes for supplying direct current to a winding of said induction motor to efiect dynamic brakin thereof.

CLAUDE B. HUSTON. 

